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\begin{equation*}
If f(x) = 3x + 7$ and $g(x) = x + 4$ then
\[ f(x) + g(x) = 4x + 11 \] 
and
\[ f(x)g(x) = 3x^2 + 19x +28. \]
\end{equation*}
\end{document}
